The Third Generation Partnership Project (3GPP) Technical Specification (TS) describes, a proxy-call session control function device (P-CSCF) as the point of contact for a user equipment (UE), such as a smart phone, to access an Internet protocol (IP) multimedia subsystem (IMS) included in a wireless wide-area network. The UE may access multimedia content via the IMS. For example, the UE may interface with the P-CSCF when exchanging, via the IMS, audio and/or video content associated with a voice over Internet protocol (VoIP), a teletypewriter (TTY), a video, or other IMS call. A component of the IMS, such as a packet gateway (PGW), may maintain a list of active P-CSCFs, and the PGW may assign one of the active P-CSCFs to the UE during registration.
As described, for example, in the 3GPP TS, several mechanisms exist for a core-initiated P-CSCF restoration in which the IMS reassigns a UE to a different P-CSCF when a failure in a P-CSCF is detected. For example, the PGW may forward an update bearer request notification that identifies active P-CSCFs (e.g., excludes a failed P-CSCF), and the UE re-registers with one of the identified P-CSCFs. However, in certain instances, connection issues between the UE and the IMS may be unrelated to a faulty P-CSCF, and restoration of the P-CSCF may not solve the connection issues. Furthermore, there may be a delay before a P-CSCF failure is detected by the IMS, and the UE will be unable to connect to the IMS to establish the IMS call or access multimedia content until the failure is detected in the IMS and a P-CSCF restoration process is implemented.